Electroconductive paper



United States Patent 3,486,932 ELECTROCONDUCTIVE PAPER Raymond J. Schaper, Pittsburgh, and Merwin Frederick Hoover, Bethel Park, P2,, assignors, by mesne assignments, to Calgon Corporation, a corporation of Delaware No Drawing. Filed Mar. 13, 1967, Ser. No. 622,443 Int. Cl. B44d 1/18; D21h 1/10 US Cl. 117-201 8 Claims ABSTRACT OF THE DISCLOSURE An electroconductive paper is described which incorporates linear acrylic polymers having pendant quaternary ammonium groups such as polymers of the formulae:

BRIEF DESCRIPTION OF THE INVENTION This invention relates to electroconductive paper, and particularly to electroconductive paper useful in electrostatic image reproduction techniques, and which has certain high molecular weight polymer coatings formed of chain units with pendant quaternary ammonium radicals.

BACKGROUND OF THE INVENTION Electroconductive paper may be used to distribute electrical stresses in various insulating products; see, for instance, United States Patent No. 3,148,107. Where electrically conductive paper is to be used for nonimpact printing, a substrate, backing, impregnation coating, or layer of electrically conductive material is usually provided. See, e.g., Vaurio and Fird, Electrically Conductive Paper for Nonimpact Printing, TAPPI, December 1964, vol. 47, No. 12, 163A-l65A.

Various types of non-impact printing processes are known, such as electrostatographic, electrophotographic, electrographic, Electrofax, and other processes. As a rule, such processes call for the placement of an electric charge on the paper. This may be accomplished by a corona discharge, for example, and in most processes, the electrical charge is placed on the paper in darkness.

The paper may also be provided with or contain a photoresponsive or photoconductive material or layer. At present there is popularly used a specially treated zinc oxide coating on the paper. Where light strikes portions of the paper treated with such a light-sensitive material, the electrical charge is dissipated in those areas exposed to the light. As a result, there is left a pattern of charged and uncharged areas.

The charged area will then -be elfective to attract an oppositely charged powdered, or other usually particulated, image-forming material. Such a powder will not be attracted to the light-affected discharged areas, and the powder may thus be deposited on the paper in a pattern to correspond with charged areas. Generally, such an image-forming material may then be fused, or otherwise treated, on the paper to make the image permanent. Such a material, presently used, is a Wax-coated finely divided carbon black, which will fuse when heated on the paper.

Other process for electrostatic reproduction differ from the above in that the image is created by electrical dis- "ice sipation of the static charge in nonimage areas. In this and certain other processes (see the Vaurio and Fird reference mentioned above), the common characteristic is again an electrically conductive base paper. This electrically conductive layer of the paper assures a rapid discharge of the charge when and where desired, and also aids in an even distribution of the initial charge.

Probably the most common copy reproduction system of the above types used at present is the direct electrostatic process; see, e.g., Chemical & Engineering News, July 20, 1964, pp. 8889 and United States Patent 3,052,- 539. This process is similar to the xerographic method for copy reproduction; however, the conductive substrate is built into the paper rather than being on a separate drum or other device. Other patents relating to conductive paper for electrostatic reproduction include 3,264,137 and 3,248,279.

The present invention provides improvements in and to the use of paper having electroconductive coatings for use in the aforesaid electrostatic copy reproduction methods.

It has now been discovered that certain polymers, generally having pendant quaternary ammonium g oups attached to an essentially linear ethylene polymer chain through an amido or ester linkage, are of special value to provide a paper substrate with an electroconductive coating. According to this invention, the polymers which may be used will generally have a molecular weight sufiicient to form clear self-supporting film of perhaps /2 to 2 microns thickness, when dried from an aqueous solution, with repeating groups of the formula:

In each case, R may represent hydrogen or a lower alkyl group such as methyl; R may represent quaternized N- methylpyridyl group or a quaternary ammonium dior trimethylene radical, e.g.:

R may also represent a quaternized ammonium grouping of aliphatic nature such as:

where X may be halogen or methosulfate.

It will be understood that in the above specifically illustrated formulae, the methyl radical of the quaternized nitrogen atom may generally be replaced by any lower alkyl group, and ethylene and trimethylene groups are also interchangeable (and other lower alkylene chains could also be used). Thus, this invention may be generally practiced with compounds of the above structures wherein R is represented as one of the formulae:

and R could be represented as 3)s wherein A is a lower alkylene group which may be substituted by an hydroxy or lower alkyl group, and R is a lower alkyl group, and, of course, it need not be the same in alkyl substituents in the quaternary group.

Polymers of this general nature have already been disclosed in the prior art, including United States Patents 2,595,907; 3,008,851; 3,014,896; 3,023,162 and 3,166,540. As is disclosed in these patents, and elsewhere in the literature, acrylic monomers, from which the above repeating units are derived, can be polymerized in an aqueous medium using a redox catalyst, as in the polymerization of acrylamide, by well-known techniques.

Illustrative of the techniques whereby the various acrylic monomers may be obtained is that wherein N-(3-dimethyl amino-propyl) acrylamide may be prepared by the reaction of acrylyl chloride (see J.A.C.S. vol. 72, pt. 2, pp. 2299-2300, May 1950) and a propylene diamine (see United States Patent No. 2,595,907). This first reaction is:

Homopolymer of 2-hydroxy-3-methacryloyloxy propyl trimethyl ammonium chloride The monomer for this example is also a known compound and is available from the following method of preparation:

Sodium Methacrylate CH3 CHzCH-CH2C1 CH -N Epichlorohydrin 1H; 01 OH: oH2=o- -o-oH2oH-o112L-N-om The intermediate compound, 2-hydroxy 3-chloropropyl methacrylate, is the subject of United States Patent 2,556,375, and the addition of trimethyl amine thereto is a well-known method of forming quaternaries.

Thus, solid 2-hydroxy-3-methacryloyloxy propyl trimethyl ammonium chloride (100 grams) was dissolved in water (400 grams). To this solution was added 0.0299 gram of ethylenediamine tetra-acetic acid, tetrasodium salt (EDTA), 0.298 gram of sodium salicylate and 0.151

Trimethylamine 4 gram nitrilotrispropionamide (NTP). The pH was adjusted to 6.5 and the solution purged for 1 hour at 50 C. After the purge, ammonium persulfate (0.075 gram) was added, and 2 minutes later a solution of sodium metabisulfate (0.75 gram) and copper sulfate pentahydrate (0.0587 gram) diluted to one liter, was pumped in at 0.1 ml. per minute. The polymerization exothermed from 48 C. to 73 C. in 60 minutes, and became extremely thick. The solution was held at 75 C. for 1 hour. The polymer solution was then diluted with water and precipitated from acetone and vacuum dried. The resulting polymer was white and extremely hydroscopic, and had an intrinsic viscosity of 3.10 in 1 N NaCl at 30 C.

Other examples of this invention are as follows:

EXAMPLE II Homopolymer of Z-methacryloxyethyl trimethyl ammonium chloride This monomer was prepared by adding dimethyl sulfate to dimethylaminoethyl methacrylate and then passing a solution of the methosulfate quaternary through an ion exchange column to place the monomer in the chloride form.

One hundred grams of this quaternary was dissolved in 400 grams of water. To the solution was added EDTA (0.0343 gram), sodium salicylate (0.341 gram) and NTP (0.174 gram). The pH was adjusted to 6.5 and purged at 50 C. for 1 hour. After the purge, ammonium persulfate (0.082 gram) was added, and one minute later a solution of sodium metabisulfite (0.855 gram) and copper sulfate pentahydrate (0.0672 gram) diluted per liter, was pumped in at 0.1 ml. per minuet. The polymerization exothermed from 49 C. to 58 C. in minutes, and became extremely thick. The viscous polymeric solution was held at 60 C. for /2 hour, and then precipitated from methanol-ether. The polymer was vacuum dried and yielded a white, solid hydroscopic polymer, which had an intrinsic viscosity of 3.625 in 1 N NaCl at 30 C.

EXAMPLE III Homopolymer of 2-acryloyloxyethyl diethyl methyl ammonium chloride This monomer was prepared by adding dimethyl sulfate to diethylaminoethylacrylate, and passing a solution of the methosulfate quaternary through an ion exchange column to place the monomer in the chloride form:

The above monomer (100 g.) was dissolved in water (400 g.). To this solution was added EDTA (0.0322 g.), sodium salicylate (0.32 g.) and NTP (0.163 g.). The pH was adjusted to 6.5, and the solution purged for 1 hour at 50 C. After the purge, ammonium persulfate (0.077 g.) was added and one minute later, a solution of sodium metabisulfite (0.803 g.) and copper sulfate pentahydrate (0.063 g.) diluted to a liter, was pumped in at 0.1 ml. per minute. The polymerization exothenned from 50 C. to 58 C. in 100 minutes, and became thick. The solution was held at 60 C. for /2 hour, and then precipitated 5 from acetone and vacuum dried in a heated dessicator to yield a solid brownish polymer, which had an intrinsic viscosity of 0.604 in 1 N NaCl at 30 C.

EXAMPLE IV Homopolymer of 3-acrylamidopropyl trimethyl ammonium chloride This monomer was prepared by adding acrylyl chloride to N,N-dimethylamino propylamine, quaternizing with dimethyl sulfate and then ion exchanging to get the monomer to the chloride form.

The quaternary salt (95 g.) was diluted with water (380 g.). To this solution was added EDTA (0.0374 g.), sodium salicylate (0.373 g.), and NTP (0.19 g.). The pH of the solution was adjusted to 6.5 and purged at 50 C. for 1 hour. After the purge, ammonium 'persulfate (0.0945 g.) was added and two minutes later a solution of sodium metabisulfate (0.945 g.) and copper sulfate pentahydrate (0.0742 g.) diluted to a liter, was pumped in at 0.1 ml. per minute. The polymerization exothermed from 51 to 65 C. in 80 minutes, and was too thick to stir. The viscous solution was held at 70 C. for 1 hour, and then precipitated by addition of acetone and vacuum dried to produce a white, hydroscopic solid, which had an intrinsic viscosity of 3.45 in 1 N NaCl at 30 C.

EXAMPLE v Homopolymer of N-(3-pyridyl) acrylamido methyl ammonium chloride -CH CH This monomer may be prepared according to the reaction scheme:

A solution of the above monomer (30%, 204.4 grams or 0.442 mole) was prepared and adjusted to pH of 6.5 and then purged at C. for 1 hour. After the purge was terminated, a solution of ammonium persulfate (5 X l0 mole catalyst/mole monomer per minute) was pumped in at 0.1 ml. per minute for 100 minutes. The polymerization exothermed from 80 to C. The solution was held at 85 C. for 1 hour and then the polymer was precipitated by addition of methanol-ether to yield a light brown solid which had an intrinsic viscosity of 0.259 in l N NaCl at 30 C.

The polymers prepared in accordance with the foregoing examples may be employed to prepare an electroconductive paper which is useful in the aforesaid electrostatic copying techniques.

To prepare such a paper, the polymers of this invention may be applied to the paper, or cellulosic web, by the conventional methods used for that purpose, e.g., coating, dipping, brushing, or by wet end addition, etc. The amount of polymer applied to the paper will generally vary within the range of about 0.5-3.0 pounds per 3,000 square feet, depending upon the particular polymer and paper combination used and the degree of electroconductivity which is desired. In some cases, still less might be used, such as, as little as 0.1 pound per 3000 square feet. There seems to be no operative upper limit to the amount of polymer applied, except to the extent this is determined by economics. It will therefore be appreciated and understood that the overall range of from about 0.1 to about 3.0 pounds per 3000 square feet is simply a statement of the required amount of polymer to confer electroconductivity properties to the cellulosic web substrate.

T o evaluate the polymer coatings provided by this invention, the following test procedure was used:

PROCEDURE FOR TESTING SURFACE RESISTIVITY The following method was employed to test the resistance to the flow of electrical current across the surface of a flat piece of material, in this case, paper.

A solution of the polymer to be tested was prepared, and filmed on paper suitable for applying electro-conductive coatings (such as Bergstroms copy paper base stock 20 lb./ream (1300 ft?) by means of a Meyer wire-wound draw rod. The amount of polymer actually coated can thus be varied by the size of the draw rod used.

The coated paper is then dried in an oven at 105 C. until dry to the touch.

After the coated paper is dry, it is conditioned in a constant conditions room for at least 16 hours.

The coated paper is placed into an environmental chamber at the desired relative humidity, and again conditioned for 24 hours.

The coated paper is then placed into the Keithly Resistivity Adapter, coated side down, a voltage (usually v.) is applied, and the electrical current passing across the surface (surface resistivity) of the sheet is read using a Keithly Electrometer.

The electrical current is read in amperes, and the following formula used to find surface resistivity:

Surface resistivity ohms/square=53.4XV/A V=applied DC. voltage A: (electrometer reading) in amperes.

Following the procedures just described, measurements were made on paper coated according to Examples IV above, and their characteristics compared with the untreated base stock and the same coated with salt humectant. The results of these comparative tests are sumelectroconductive properties to the paper substrate, as those skilled in the art will obviously appreciate.

This invention is, accordingly, believed to be limited only by the spirit and scope of the following claims which are intended to set forth and define the contribution of marized in the following Table 1. 5 the art consisting essentially of providing the defined TABLE 1 Surface Surface Surface Surface Surface Surface Meyer Coating amperage at resistivity at amperage at resistivity at amperage at resistivity at rod, weight, 5% relative 5% relative 22% relative 22% relative 54% relative 54% relative Example mils lb./3,000 it. humidity humidity humidity humidity humidity humidity Salt humectant 3 0. 7 10- 10 .42 10 1. 3x10 90 10- 5. 9x10 22 2. 6 10- 10 18 10 3. 10 .23 10 2. 3X10 40 4. 4 10- 10 19x10 2. 8X10 .21 10- 2. 5 10 Untreated base stock .21 10 2. 5 10 s9 10- 6.0)(10 I 3 0. 4 75 1o 7. 1x10 13 1o- 3. 0x10" 1s 10- a. 0x10 22 1. 1 65 10- 13.2 10 11 10 4. 9x10 s6 10 0. 2x10 40 1. 7 10x10- 5. 3X10 13x10- 4. 1x10 12x10- 4. 5x10 II 3 0. 4 70x10- 7. s 10 12x10- 4. 5 10 5s 10 9. 5x10 22 0. 9 50 10 1. 1 10 61x10- s. s 10 2s 10- 1. 9x10 40 1. 6 72x10- 7. 4x10 10 10- 5. 3x10 45 1o- 1. 2x10 111 3 0. 3 s0 10 87 9x10 24 10- 2. 2 10 13x10- 4.1 10 22 1. 0 26 10- 2. 1 10 21 10 2. 5x10 90 10 5. 9x10 40 1.8 13 10 4. 1x10 .85X10'5 6. 3 10 a3 10- 1. 6X10 IV 3 0. 4 00x10- 5. 9x10 .14 10- 3. s 10 68 l0- 7. 9 10 22 1. 1 30 10- 1. s 10 .39 10 1. 4x10 17 10 3.1 10 40 1. 7 45 10 1. 2 10 52x10- 1. 0 10 28 10 1. 9x10 V 3 0. 3 10 10- 5. 3X10 77 10- 6. 9x10 41 10- 1. 3x10 22 1. 2 30 10- 1. s 10 .40 10 1. 3x10 12x10- 4. 5x10 It will be appreciated from the foregoing Table 1 that 25 polymers as the essential electroconductive coating comthe coated paper provided by this invention has Signifiponent on copy paper having superior characteristics as cantly improved conductive characteristics, particularly described hereinabove. at low humidity conditions. This latter feature is of special What is claimed is: importance inasmuch as it is the generally prevalent con- 1. An electroconductive paper having incorporated dition in relatively hot copy machines, and, accordingly, thereon a coating composition containing as the essential technically satisfactory copy paper must have adequate electroconductive component thereof, at least one linear, conductivity characteristics especially in the lower hufilm-forming, water-soluble cationic polymer having remidity ranges. peating chain units of the formula:

While in the Table 1 the coating thickness is indicated by the notation of the Meyer rod measurement in mils I I l (which is the thickness of the liquid coating at the point -CHQC -CHzC- it was laid down), it will be appreciated that the dried (13:0 or 5 coating weight is actually more pertinent and significant. 1 Surface amperage measurements have also been included, although it is the surface resistivity measurements wh1ch R R, are of the greatest technical importance. h i

The salt humectant treatment noted in the first entrles R stands f hydrogen or lower alkyl; of the table is a conventional coating which has been R1 represents a member of the Class Composed f employed, and consists of an aqueous solution of 8% R potassium chloride and 0.1% hydroxyethyl cellulose (as 0 g a the composition is applied to the paper). or

The polymer coatings according to the present inventron were la1d down on the paper from an aqueous solu- R2 Stands for non having a concentration of about 4% polymer.

It will thus be seen that this invention provides an advantageously improved electroconductive paper which has h t A t 1 1k 1 incorporated thereon a coating composition which con- W g a k ll'epresen 10:, l 'k l gb t Pt t g tains as the essential electroconductive component thereof i l a y ens t 2' y 2 S 1 i a high molecular weight, water soluble, cationic polymer gig 3;? y ens group an 3 S an S r a Wer a y e hain units of the formula: havm repeated 6 wherem said coated paper has a surface res1st1v1ty at about 50% relative humidity of the order of about I" R I l- R "I 10 -10 ohms/square; a surface resistivity at about g J; 22% relative humidity of the order of about10 l() or ohms/ square; and a surface resistivity at about 5% humidity of the order of about 10 -10 ohms/ I I square. R1 )1 Ba x 2. The coated paper of claim 1, wherein said polymer is of the formula: I In this formula, the symbols R and R have the sigon; "I nificance already indicated above, and the symbol x signifies the number of such chain units in the polymer 6 molecule. The mode of application of such electrocon- O=C O CHZCHOHQHQN M: ductive polymer component to the paper does not form 3. The coated paper of claim 1, wherein sa1d polymer is of the formula:

9 10 4. The coated paper of claim 1, wherein said polymer 8. The coated paper of claim 1 wherein said polymer is of the formula: is presented in the coating in a required amount of from about 0.1 to about 3.0 pounds per 3000 surface square -CHgCH-- feet of said paper.

L J 5 References Cited o=o0 omonzmomcmn, 01

UNITED STATES PATENTS 5. The coated paper of claim 1, wherein said polymer I 2,807,910 10/1957 Erickson.

is of the formula: 6

3,125,550 3/1964 Laakso etal 260-295 LCHFCH 10 3,216,853 11/1965 Gess 117-201 e 9 3,264,137 8/1966 Gess 117 20 1 01 3,295,967 1/1967 Schoenfeld 117-152 6. The coated paper of claim 1, wherein said polymer is of the formula: O EIGN ATENTS 15 1,015,795 1/1966 Great Britain.

CHr-CH l ALFRED L. LEAVITT, Primary Examiner O=0-NH- 01 C. K. WEIFFENBACH, Assistant Examlner 2 US. 01. X.R.

7. The coated paper of claim 1 wherein said polymer 117152 154; 260F785 has a molecular weight sufiicient to enable it to form clear, self-supporting film of from about /22 microns thickness when dried from an aqueous solution. 25 

